Electromagnetic joystick using varying overlap of coils and conductive elements

Abstract

A joystick having an electromagnetic element coupled to a movable stick, with at least a pair of orthogonal coils on an underlying substrate. Alternately, the coils and electromagnetic elements can be reversed. The movement of the stick is detected by the amount of overlap of the electromagnetic element and the coils in each direction. The quality factor of the coil changes as more or less of the coil is overlapped, which can be measured by an electric circuit to determine the direction of movement and the amount of movement of the joystick. The electromagnetic element could be, for instance, a conductive steel plate, or a piece of another metal or of another conductive material, or ferrite particles. The coil could be wound (preferably on air only or, if needed to reach a higher value of inductance, on a magnetic core, provided this is small enough to not hide the effect of the mobile electromagnetic element). Or the coils could be made from traces on a printed circuit board (PCB), provided the use of a high enough (greater than 1 MHz) driving frequency, eliminating the need for a large, expensive wound coil.

What is claimed is: 
     
       1. A joystick comprising: a stick mounted to allow movement;   first and second coils arranged at orthogonal positions with respect to said stick;   first and second electromagnetic members each connected at one end to said stick, such that as said stick moves in line with one of said members, an amount of overlap of said electromagnetic member over one of said coils varies due to movement of said stick.   
     
     
       2. The joystick of claim 1 wherein said overlap is varied by a translational movement of said electromagnetic member parallel to said coil. 
     
     
       3. The joystick of claim 1 wherein said overlap is varied by a rotating movement of said electromagnetic member. 
     
     
       4. The joystick of claim 3 wherein said first and second members comprise V-shaped elements connected to said stick by first and second arms, respectively. 
     
     
       5. The joystick of claim 1 wherein said overlap is varied by a flexing of said electromagnetic members. 
     
     
       6. The joystick of claim 5 wherein each of said electromagnetic members have a first end connected to said stick, and a second end connected to a platform supporting said first and second coils. 
     
     
       7. The joystick of claim 1 further comprising an electric circuit for providing an output signal corresponding to movement of said stick, said electric circuit being mainly responsive to a change in quality factor of said coils. 
     
     
       8. The joystick of claim 1 further comprising: third and fourth coils opposite said first and second coils, respectively; and   third and fourth electromagnetic members each connected to said stick and being positioned over said third and fourth coils, respectively.   
     
     
       9. The joystick of claim 8 further comprising an electric circuit for providing differential output signals corresponding to a difference between the quality factor of said first and third coils, and the difference between the quality factor of said second and fourth coils. 
     
     
       10. The joystick of claim 8 further comprising an electric circuit for measuring the quality factor of each coil and a digital calculator for computing differences between individual output signals corresponding to a difference between the quality factor of said first and third coils, and the difference between the quality factor of said second and fourth coils. 
     
     
       11. The joystick of claim 1 wherein said electromagnetic members also provide a centering force for said stick. 
     
     
       12. The joystick of claim 1 further comprising an insulating layer between said coils and said electromagnetic members. 
     
     
       13. The joystick of claim 1 wherein said electromagnetic members comprise steel plates. 
     
     
       14. The joystick of claim 1 wherein said electromagnetic members comprise a nonconductive substrate containing ferrite particles. 
     
     
       15. The joystick of claim 1 wherein said first and second coils are traces on a printed circuit board. 
     
     
       16. The joystick of claim 9 wherein second ends of said electromagnetic members are connected to said printed circuit board, such that each of said members is in contact with a portion of a corresponding one of said coils in a rest position. 
     
     
       17. The joystick of claim 16 wherein an overlapped portion of said coils varies between 10-25 percent minimum overlap and 75-90 percent maximum overlap. 
     
     
       18. The joystick of claim 1 further, comprising: a plurality of capacitors, each coupled to one of said coils to form a resonant circuit;   an oscillator driver coupled to said coils for driving said resonant circuits; and   an impedance measuring circuit coupled to a node between said resonant circuits and said oscillator driver.   
     
     
       19. The joystick of claim 1 further, comprising: a single capacitor, coupled to each of said coils when it is selected for measurement, to form a resonant circuit;   an oscillator driver coupled to said coils for driving said resonant circuits; and   an impedance measuring circuit coupled to a node between said resonant circuits and said oscillating driver.   
     
     
       20. The joystick of claim 1 further comprising: a plurality of capacitors, each coupled to one of said coils to form a resonant circuit;   an oscillator driver coupled to said coils for driving said resonant circuits, said oscillator having a frequency of at least one MHz; and   wherein said coils comprise traces on a printed circuit board.   
     
     
       21. The joystick of claim 1 further comprising: a single capacitor, coupled to each of said coils when it is selected for measurement, to form a resonant circuit;   an oscillator driver coupled to each of said coils for driving said resonant circuits, said oscillator having a frequency of at least one MHz; and   wherein said coils comprise traces on a printed circuit board.   
     
     
       22. A joystick comprising: a stick mounted to allow movement;   a printed circuit board having first and second coils arranged at orthogonal positions with respect to said stick;   first and second electromagnetic members each connected at one end to said stick, such that as said stick moves in line with one of said members, an amount of overlap of said electromagnetic member over a corresponding one of said coils varies due to movement of said stick;   third and fourth coils opposite said first and second coils, respectively;   third and fourth electromagnetic members each connected to said stick and being positioned over said third and fourth coils, respectively; and   an electric circuit for providing differential output signals corresponding to a difference between the quality factor of said first and third coils, and the difference between the quality factor of said second and fourth coils.   
     
     
       23. A joystick comprising: a stick mounted to allow movement;   a substrate having first and second electromagnetic elements arranged at orthogonal positions with respect to said stick;   third and fourth electromagnetic elements, each connected at one end to said stick, such that as said stick moves in line with one of said members, an amount of overlap of one of said third and fourth elements over one of said first and second elements varies due to movement of said stick;   wherein two of said elements are coils, and the other two of said elements are an electromagnetic member.   
     
     
       24. An electric circuit for measuring the movement of a joystick, wherein said joystick includes electromagnetic elements and coils with relative movement between them, comprising: a plurality of capacitors, each coupled to one of said coils to form a resonant circuit;   an oscillator driver coupled to said coils for driving said resonant circuits; and   an impedance measuring circuit coupled to a node between said resonant circuits and said oscillator driver.   
     
     
       25. An electric circuit for measuring the movement of a joystick, wherein said joystick includes electromagnetic elements and coils with relative movement between them, comprising: a single capacitor, coupled to each of said coils when it is selected for measurement, to form a resonant circuit;   an oscillator driver coupled to said coils for driving said resonant circuits; and   an impedance measuring circuit coupled to a node between said resonant circuits and said oscillator driver.   
     
     
       26. The electric circuit of claim 24 wherein said coils comprise traces on a printed circuit board. 
     
     
       27. The electric circuit of claim 24 wherein said resonant circuits have a resonant frequency different than a frequency of said oscillator driver. 
     
     
       28. The electric circuit of claim 24 wherein a frequency of said oscillator driver is between one and eight MHz. 
     
     
       29. An electric circuit for measuring the movement of a joystick, wherein said joystick includes electromagnetic elements and coils with relative movement between the electromagnetic elements and the coils, comprising: a plurality of capacitors, each coupled to one of said coils to form a resonant circuit;   an oscillator driver coupled to said coils for driving said resonant circuits, said oscillator having a frequency of at least one MHz; and   wherein said coils comprise traces on a printed circuit board.   
     
     
       30. An electric circuit for measuring the movement of a joystick, wherein said joystick includes electromagnetic elements and coils with relative movement between the electromagnetic elements and the coils, comprising: a single capacitor, coupled to each of said coils when it is selected for measurement, to form a resonant circuit;   an oscillator driver coupled to said coils for driving said resonant circuits, said oscillator having a frequency of at least one MHz; and   wherein said coils comprise traces on a printed circuit board.   
     
     
       31. A position input device for a personal computer that offers a similar function as a mouse for controlling the movement of a cursor on the screen, wherein said input device comprises: a plurality of coils formed as traces on a printed circuit board;   at least one capacitor coupled to said coils;   electromagnetic elements positioned to allow relative movement between said coils and said electromagnetic elements;   an oscillator driver coupled to said coils, said oscillator having a frequency of at least 1 MHz; and   means for measuring the impedance of resonant circuits formed by said coils and said at least one capacitor, such that relative movement is detected by the effect it causes on the quality factor of each coil.   
     
     
       32. A position input device for electronic gaming station, wherein said input device includes: a plurality of coils formed as traces on a printed circuit board;   at least one capacitor coupled to said coils;   electromagnetic elements positioned to allow relative movement between said coils and said electromagnetic elements;   an oscillator driver coupled to said coils, said oscillator having a frequency of at least 1 MHz; and   means for measuring the impedance of resonant circuits formed by said coils and said at least one capacitor, such that relative movement is detected by the effect it causes on the quality factor of each coil.   
     
     
       33. The position input device of claim 32 wherein said device is one of a game steering wheel, a game rudder and a game pad.